The human body contains a wide variety of natural valves, such as, for example, heart valves, esophageal and stomach valves, intestinal valves, and valves within the lymphatic system. Natural valves may degenerate for a variety of reasons, such as disease, age, and the like. A malfunctioning valve fails to maintain the bodily fluid flow in a single direction with minimal pressure loss. An example of a malfunctioning valve is a heart valve that may be either stenotic, i.e., the leaflets of the valve do not open fully, or regurgitant, i.e., the leaflets of the valve do not close properly. It is desirable to restore valve function to regain the proper functioning of the organ with which the valve is associated. For example, proper valve function in the heart ensures that blood flow is maintained in a single direction through a valve with minimal pressure loss, so that blood circulation and pressure can be maintained. Similarly, proper esophageal valve function ensures that acidic gastric secretions do not irritate or permanently damage the esophageal lining.
Several percutaneous prosthetic valve systems have been described. One example described in Andersen, et. al. (U.S. Pat. No. 5,411,552) comprises an expandable stent and a collapsible valve which is mounted onto the stent prior to deployment. Spenser, et. al. (U.S. Pat. No. 6,893,460) describe another prosthetic valve device comprising a valve structure made of biological or synthetic material and a supporting structure, such as a stent. The Spenser prosthetic valve is a crimpable leafed-valve assembly consisting of a conduit having an inlet and an outlet, made of pliant material arranged to present collapsible walls at the outlet. The valve assembly is affixed to the support stent prior to deployment. The complete valve device is deployed at a target location within the body duct using a deploying means, such as a balloon catheter or a similar device. Percutaneous implantation of medical devices, particularly prosthetic valves, is a preferred procedure because it allows implantation without the need for opening a large portion of the chest.
Accurate placement of current percutaneous valve devices relative to the existing native anatomy is often problematic, particularly in the case of aortic valve replacements. Consequences of poor valve placement in the case of an aortic valve include functional and/or physical occlusion of the orifice of the coronary artery distal to the aortic valve, and/or increased pressure on and disruption of the electrical conduction apparatus of the heart. Specifically, a prosthetic valve that is placed too distally (i.e., toward the aorta) can occlude or impede flow into the orifices of the coronary arteries. For example, depending on the position of the coronary ostia, either the skirt of the prosthetic valve or large native valve leaflets pressed down against the aorta wall may physically or functionally obstruct the orifices and impede coronary arterial flow. See, e.g., Piazza, N., et al., “Anatomy of the Aortic Valvar Complex and Its Implications for Transcatheter Implantation of the Aortic Valve,” CIRCULATION CARDIOVASCULAR INTERVENTIONS, 1:74-81 (2008); Webb, J G, et al., “Percutaneous aortic valve implantation retrograde from the femoral artery,” CIRCULATION, 113:842-850 (2006). This obstruction may be either physical or it may be functional, i.e., the orifices of the coronary arteries are physically patent, but due to alterations in flow patterns produced by the prosthetic valve, flow into the coronary arteries is partially impeded. A prosthetic valve that is placed too proximally (i.e., toward the ventricular outflow tracts of the left ventricle) can interfere with the anterior leaflet of the Mitral valve, the atrioventricular node or the bundle of His (conduction tissues). Approximately thirty percent of patients receiving prosthetic valves percutaneously require pacemakers, because the valve is placed with the ventricular end too close to or on top of the left bundle branch, putting pressure on the electrical conduction apparatus. See, e.g., Piazza, N., et al., “Early and persistent intraventricular conduction abnormalities and requirements for pacemaking following percutaneous replacement of the aortic valve,” JACC CARDIOVASCULAR INTERVENTIONS, 1:310-316 (2008); Piazza, N., et al., “Anatomy of the Aortic Valvar Complex and Its Implications for Transcatheter Implantation of the Aortic Valve,” CIRCULATION CARDIOVASCULAR INTERVENTIONS, 1:74-81 (2008).
Persons of skill in the art recognize that one limitation on percutaneous prosthetic aortic valve replacement methods using currently available pre-assembled valve devices is a less than desirable level of precision for positioning the valve. See Ussia, G. P., et al., The “Valve-in-Valve Technique: Transcatheter Treatment of Aortic Bioprosthesis Malposition,” CATHETERIZATION CARDIOVASCULAR INTERVENTIONS, 73:713-716 (2009); Ghanbari, H., et al., “Percutaneous Heart Valve Replacement: An Update,” TRENDS CARDIOVASCULAR MEDICINE, 18:117-125, (2008); Lutter, G., et al., “Percutaneous Valve Replacement: Current State and Future Prospects,” ANNALS THORACIC SURGERY, 78:2199-2206 (2004).
Repositioning methods have been proposed. Such methods involve a repositioning of the entire valve device rather than adjustment from the previous position. One method of repositioning a percutaneous prosthetic valve involves compressing or relaxing the stent that serves as the frame for the valve. See Zegdi, R. et al., “A Repositionable Valve Stent for Endovascular Treatment of Deteriorated Bioprostheses,” J. AMERICAN COLLEGE CARDIOLOGY, 48(7):1365-1368 (2006). Such a method provides little if any fine control over the axial position or angular position of the valve, and risks significant shifting of the entire device and/or damage to the tissue. Another method of repositioning a percutaneous prosthetic valve involves preventing the stent from fully expanding until it is in position, or unexpanding the stent slightly in order to reposition it. Buellesfeld, et al., “Percutaneous Implantation of the First Repositionable Aortic Valve Prosthesis in a Patient with Severe Aortic Stenosis,” CATHETERIZATION CARDIOVASCULAR INTERVENTIONS, 71:579-584 (2008); US Published Application No. 2005/0137688A1 to Salahieh et al. Such a method provides little if any fine control over the axial position or angular position of the valve, and repeated expansion and compression of the stent at or near the site of implantation risks damage to the tissue.
Therefore, there is a need in the art for an apparatus and method for making fine adjustments to a valve's position after implantation—i.e., to move the valve in small increments until the proper position is achieved. This adjustment method provides an iterative feedback process where each adjustment is an incremental improvement over the last position. A need also exists for a method of delivering a prosthetic valve with increased safety, e.g., with minimal damage to the vessel wall and with good control of the adjustment process. A device that can be placed in the vessel without incurring further damage to the wall of the body lumen during delivery and/or during adjustment of the valve position—e.g., adjusting the valve, not the frame—is highly desirable.